I. Field
The following description relates generally to wireless communications, and more particularly to redirecting user equipment from long term evolution networks.
II. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
With respect to LTE networks, it is noted that initial LTE deployments by 3GPP operators will be in pockets. As a result, the user equipment (UE) might run out of LTE coverage while active on the LTE network and will have to move to a High Rate Packet Data (HRPD)/1X network to continue service. In addition, initial LTE deployments will not support a voice-over-internet-protocol (VoIP). One solution being proposed is for the UE to fallback to the 1X network for making and receiving voice calls (referred to as 1XCSFB).
Initial LTE networks will use a redirection based approach to move the UE to HRPD/1X upon recognizing that the UE is moving out of LTE coverage. This command currently specifies a single band/channel in which the target radio access technology (RAT) will be found. A similar redirection command is used in 1XCSFB. The current structure of the current redirection message, however, only allows the LTE network to specify a single frequency. Having a single frequency in the redirection message can lead to several reliability issues. For example, since the single specified carrier could experience a fade while another carrier has good coverage in the UE's current location, it has been shown to decrease handover reliability. Using just one frequency thus fails to exploit the operator's universal data-optimized (DO)/1X coverage. Also, since LTE is deployed in a lower frequency, a single LTE cell might span multiple DO/1X cells. In this case the best sectors/frequency will vary considerably depending on the UE's location in the LTE cell. Specifying a single frequency will be even more suboptimal in terms of reliability in this case.
Specifying a single frequency also undesirably adds to delay. For example, many UEs may have to hash-to another frequency after acquiring the DO/1X system on the single redirected frequency. Also, after moving to the frequency, the UE may have to update its overhead message, which prevents optimizations like cached overhead messages.
The above-described deficiencies of current wireless communication systems are merely intended to provide an overview of some of the problems of conventional systems, and are not intended to be exhaustive. Other problems with conventional systems and corresponding benefits of the various non-limiting embodiments described herein may become further apparent upon review of the following description.